Electronic loads are used in a variety of industries particularly for testing electrical or electronic equipment such as power supplies, batteries, solar cells, cell phones, communication systems, among an assortment of other types of circuitry and devices. An electronic load is a device that simulates loading on an electronic circuit in lieu of a traditional ohmic load resistor. Contrary to a current source, the electronic load is traditionally used as a current sink. The electronic load generally consumes electrical energy and transforms it into another form of energy, such as heat.
Some electronic loads provide different operating modes such as constant current, constant voltage, constant power, or constant resistance modes. For instance, the electronic load can receive a user settable resistance value and operate in a constant resistance mode in which either the voltage or current in the circuit is sensed, and the current or voltage is adjusted, respectively, to maintain the resistance designated by the user. In other words, if the voltage is sensed by the electronic load, then the current can be driven by the electronic load to maintain a form of constant resistance within the electronic load. Similarly, if the current is sensed by the electronic load, then the voltage can be driven by the electronic load to maintain a form of constant resistance within the electronic load. The relationship between the current, voltage, and resistance can be maintained as a result of Ohm's law.
In the constant resistance mode, there is a small delay introduced between the time of sensing the control variable and the time of driving the controlled variable. The delay is usually on the order of nanoseconds or microseconds, and is inherently dependent on the processing time or propagation time of circuitry used in sensing and controlling the signal under test. Depending upon whether the current is measured, and the voltage controlled, or the voltage measured, and the current controlled, such delay can cause a reactive component to the load to look slightly capacitive or slightly inductive, respectively. Such delay is not specified in the industry, and while known to some, it is generally thought of as a flaw in the system.
It would be desirable to have an electronic load in which control is provided over the propagation delay in order to model the reactive component to the load. Accordingly, a need remains for an improved method and apparatus for providing variable reactive load capability on an electronic load.